In generations past, horses were abandoned or shipped off to slaughter once it was decided that they had worn out their usefulness in pulling wagons or plows and in carrying loads or people: think of poor Boxer, carried away by a van marked “Alfred Simmonds, Horse Slaughterer and Glue Boiler” toward the end of George Orwell’s Animal Farm. Today, some horses are sentenced to die because they are of no more use to pharmaceutical companies that make fortunes dispensing medicines to consumers, most notably the drug Premarin.

In the 1940s, researchers at one drug firm discovered that estrogen taken from the urine of pregnant mares helped to relieve some of the effects of menopause in women. Overnight, an industry sprang up in the northern United States and Canada as hundreds of farms were placed under contract to deliver this urine.

More than sixty years later, it remains an industry. As if on an assembly line, mares are impregnated and placed in narrow stalls; the industry-mandated stall width is 3.5 feet (about 1.1 meters) for horses weighing less than 900 pounds (410 kg) and 5 feet (1.5 meters) for those exceeding 1,700 pounds (770 kg), whereas the usual dimension of a stall at a regular stable is at least twice that size.

Fitted with collection bags, the mares are regularly deprived of water in order to concentrate their urine. Or so it is believed, in any event; there is no way of telling whether the 1940s-era practice continues, since the industry stonewalls such inquiries. The Humane Society of the United States reported in 2007, “The pharmaceutical company now claims that the water restriction policy has been modified; however, they remain unwilling to allow humane organizations access to the farms to verify such changes.”

After giving birth to their foals, the mares are impregnated again and returned to the stalls, while most of the foals are slaughtered for meat. So, too, are the mares once their bearing years have passed.

In most particulars, in other words, and in more than half a century since its inception, little has changed in the Premarin industry—for the horses, that is. In 2002 a study by the Women’s Health Initiative, part of the National Institutes of Health (NIH), linked the long-term use of Premarin to an increased risk of stroke and blood clots, and the use of the related drug Prempro to elevated rates of heart disease and breast cancer. The NIH advised physicians to cease prescribing the drugs;sales fell, and some 350 PMU (pregnant mares’ urine) farms lost their contracts over the next two years, while thousands of lawsuits were filed against the manufacturer.

Yet the drug is still made and sold; indeed, the FDA recently gave the manufacturer permission to market a new Premarin-based drug meant to treat osteoporosis as well as menopause. Says the Pharmaceutical Business Review, “This would open up bazedoxofine/Premarin therapy to the whole postmenopausal market while providing a continuum of care throughout the menopausal period.” Even with the health scare, the market for Premarin and allied PMU-based drugs is estimated to exceed $1.2 billion; the market for the new combined product, the article continues, is expected to exceed $550 million by 2010.

An unknown number of farms, most in the Canadian province of Manitoba, continue to serve as urine factories—halfway houses to the slaughterhouse or an early grave in all events. A study in the Canadian Veterinary Journal, for instance, reports that nearly one in four of the foals born on PMU farms in western Manitoba in a single year died of starvation or exposure.

Opposition to the PMU industry has been strong since the 1990s, spearheaded by the American Society for the Prevention of Cruelty to Animals (ASPCA), which decried it as “unthinkable and unforgivable.” Mere outrage has not proved particularly effective, however. What has brought exposure to the problem is the work of PMU rescue groups and adoption agencies such as Crooked Pine Animal Rescue of Dudley, N.C.; Equine Voices, headquartered in southern Arizona; and Canyon Creek Farm of Acton, Calif. Says Karen Pomroy of Equine Voices, “We have so much to do. In 2005 we rescued 43 horses at one time from PMU farms that were closing down. Now the manufacturer forbids anyone who signs a contract to produce PMU from dealing with rescue groups, so we’ll probably have to start bidding against the slaughter industry to get the mares and foals out.”

Another strategy—one that is gathering momentum—is to emphasize that Premarin is not the only remedy for troublesome menopausal symptoms. The FDA has approved several plant-derived and synthetic estrogens as safe and effective, and some are thought to be superior to Premarin in both performance and patient tolerance. Some patients who have made the switch, advocates report, have encountered initial resistance from insurance companies, but others have made converts of their doctors in the process, helping to slowly spread the word about the unnecessary suffering of the Premarin-industry horses.